Streaming Video | Ipod-friendly Download

Back to Notes

4.1.3.       Interference & Wave Nature of Light  <CJ chap  27 >

4.1.3.1. Discussion

4.1.3.1.1.     Principle of linear superposition: resultant disturbance is the sum of separate disturbances

4.1.3.1.2.     Interference is constructive if waves are in phase, destructive otherwise 

4.1.3.1.3.     Thin film interference described as with gasoline on water

4.1.3.1.4.     Diffraction through a slit: resolving power is when the first dark band falls on the central bright band

4.1.3.1.5.     Diffraction grating – used to diffract light and create a spectroscope

4.1.3.2. Mathematical

4.1.3.2.1.     Young’s double slit experiment: sin q = m(l/d) constructive with m = 0, 1, 2; destructive m = 1/2 , 3/2..

4.1.3.2.2.     Thin film l_film = l_vacuum /n   and

4.1.3.2.2.1. thus difference of distance = 2thickness + ½ l_film (due to reflection) =½ l_film , 3/2 l_film…

4.1.3.2.2.2. then subtracting ½ l_film from each side one gets 2 t = 0, 1l_film , 2l_film ,  3l_film …

4.1.3.2.2.3. then solving for t one gets  t = m l_film /2  where m = 0, 1, 2, 3, …

4.1.3.2.3.     Diffraction through a single slit gives:  sin q = m l /W where m = 1, 2, …, W=width, for destructive intr

4.1.3.2.3.1. q_min = 1.22 l/D for the minimum resolution between two objects using an aperture D

4.1.3.2.3.2. Diffraction grating maxima are  sin q = m l/d   m = 1, 2, 3 where d is the slit separation

4.1.3.2.3.2.1.     red is dispersed by the greatest angle and violet the least

4.1.3.3. Advanced